Physics of Atomic Nuclei and Elementary Particles

Abstract

From the standpoint of a rigid systematical approach, a discussion of the atomistic structure of matter should begin with a discussion of the elementary particles and atomic nuclei. Then atomic physics in its more restricted sense, molecular physics, and physics of the solid state would logically be built up on the theory of the structure of atomic nuclei. In presenting Bohr’s pictorial atomic physics first, we have followed the historical development and, at the same time, had the advantage of proceeding from the simpler to the more difficult. Historically, up to about 1927, the first field to be studied and explained was physics of the atomic shells. Then further development led, on the one hand, to a theory of molecules which are composed of a number of atoms as well as to a theory of larger atomic complexes (liquids and solids) and, on the other hand, to nuclear physics. For this development, it was necessary to have the knowledge of Bohr’s atomic theory and its quantum-mechanical refinements which we discussed in the last chapter. The same applies to our presentation in this book. Energy states and the transitions between them, accompanied by radiation, occur in the nucleus (though with correspondingly larger amounts of energy) just as in the electron shells of the atom. It is impossible to understand essential processes such as the decay of nuclei or the exchange forces which cause the bond between the nuclear constituents without a knowledge of quantum mechanics. It thus seems reasonable, both from the standpoint of an intelligible introduction as well as from that of the actual development of our science, to discuss nuclear physics at this point.